As a Ph.D. candidate in Durham, England, back in 1983, assessing Caribbean evolution with John Dewey, I had a far-reaching decision to make:
Were there enough arguments to champion a firm stand for a Pacific origin of the Caribbean lithosphere, as Kevin Burke, Bruce Malfait and others had suggested?
At that time I had just quantified for the first time the American relative plate motion histories with respect to Africa using Seasat/Geosat data – with Steve Cande and Walter Pitman at Lamont, in 1981-82 – so I was in a good position to test hypotheses concerning Caribbean origin.
Through the course of compiling information for my thesis – and guided by the plate kinematics – the answer to the question, even back then, was an overwhelming “yes.”
Drift between North and South America created Jurassic-Cretaceous “Proto-Caribbean” passive margins, which were subsequently overrun by allochthonous Caribbean oceanic/arc terranes. I was able to show, by evaluating the circum-Caribbean foredeep basins, the eastward-younging history of oblique arc-continent collision from the Pacific since the Campanian, when Caribbean lithosphere first arrived along southern Mexico/Chortis and western Colombia from even farther west.
It also was apparent that the Caribbean lithosphere has rested very nearly in the hot spot or mantle reference frame since before the Cenozoic, such that the American plates, and not the Caribbean, have caused the relative plate motion as the Americas have drifted west from Africa to form the Atlantic.
Today, arguments for this story are more numerous and better documented than in 1985, and none contest it.
♦ A conspicuous aspect of Caribbean geology explained only by an allochthonous Caribbean origin is the paucity of arc-related tuffs in the Cretaceous Proto-Caribbean passive margin sections of Yucatán, Bahamas, northern Colombia, Venezuela and Trinidad.
In contrast, the Caribbean arcs were constantly eruptive, and deposition across the Caribbean Plate was dominated by arc tuffs. Clearly, there was significant spatial separation between the arcs and the passive margins in the Cretaceous, unlike more recent times.
Further, Proto-Caribbean passive margin sections are separated today from Cretaceous-Paleogene mobile belts of arc magmatism, tectonic deformation and subduction-related HPLT metamorphic rocks and mélanges, by the circum-Caribbean suture (figure 1, black).
These abrupt juxtapositions are clearly incompatible for Cretaceous-Early Paleogene time, and the respective associations could not have formed near each other.
♦ East- west opening of the Cayman Trough, a hyper-extended pull-apart basin along the northern Caribbean boundary, is at least 700 kilometers – and more likely about 1,000 kilometers – judging from the basement’s oceanic spreading fabric and trough-flanking structure. This has occurred since at least the Oligocene (dredged basin floor sediments) or the Eocene (magnetic anomaly interpretation).
But this 700-1,000-kilometer estimate of American-Caribbean relative motion (figure 1, blue) comprises only part of the estimate derived from seismic tomography, which images the Atlantic slab dipping westward some 1,500 kilometers beneath the eastern Caribbean Plate (figure 1, red).
Fifteen-hundred kilometers is a measurable minimum Caribbean-American Tertiary displacement.
♦ Caribbean lithosphere has rested nearly in the hot spot reference frame since subduction and arc magmatism began along the western, Costa Rica-Panama Caribbean margin in the Campanian, such that the plate has been locked between opposing subduction zone “anchors” that have moved laterally very little through the mantle.
Unlike North and South America, with their Cretaceous-present histories of compressive orogenesis along their western subduction systems, the Caribbean does not drive westward over the mantle, because subduction at the Lesser Antilles matches American westward drift. The Costa Rica-Panama Arc is not being thrust over the trace of its own trench, and thus there has been no Cenozoic Andes-type orogenesis in Costa Rica-Panama.
Further, migration paths of North America relative to the hot spots closely scribe the Cayman Trough in both azimuth and length, especially if we accept an Eocene time of initial Cayman Trough opening (figure 1, pink). This is strong evidence that the Cayman Trough does indeed record American-Caribbean relative motion.
An implication of 1,000 kilometers of Cayman Trough opening is that Jamaica restores to a position near the southeastern Yucatán Block in the Eocene. Jamaica’s Richmond Fm conglomerates bear metamorphic clasts that appear to derive from Central America rather than Jamaica itself.
Simon Mitchell, Uwe Martens and I are currently examining this material for lithologic and chronologic ties to the Chuacus and other metamorphic units of Central America.
Another implication of 1,000 kilometers of Cayman Trough opening is that the displacement also must occur obliquely through the Greater Antilles Arc. Sinistral segmentation of Antillean rock units on the order of 300, 400 and 300 kilometers at the Oriente, San Juan-Muertos and Anegada fault zones, respectively, are apparent and consistent with Cayman displacement (figure 1).
♦ The Greater Antilles Arc collided with the Bahamas above a southwest-dipping subduction zone in the Eocene. The same subduction zone was responsible for the Neocomian to Eocene history of arc magmatism and HPLT subduction-related metamorphism, some 80 million years.
Following the tenet that arcs need subduction rates of >20 mm/year to evolve robustly, the Antilles Arc likely migrated from the southwest by at least 1,600 kilometers prior to the Eocene collision (figure 1, strawberry). This pre-dates Cayman Trough opening and places the arc, with the Caribbean Plate southwest of it, west of Colombia and south of Yucatán, in the Pacific.
But 1,600 kilometers is only a minimum, because the arc did not begin to collide with Yucatán until 80 Ma.
Further, in the Neocomian when Greater Antillean arc magmatism and subduction began, the gap between the Americas was trivial (figure 1, white), with no “room” (or reason) for Antillean subduction to begin within this entirely extensional passive margin setting.
♦ Recent and ongoing field and lab studies by Tectonic Analysis and others are strengthening the long-held suspicion that rocks of the Chortis Block (nuclear Central America) are equivalent to and originated from a position along the Acatlán/Oaxaca complexes of southern Mexico. This implies about 1,600 kilometers of Chortis displacement (figure 1, green), larger than the width of onshore central Guatemala, such that there can be no strike-slip offset marker there.
It also is greater than the length of Cayman Trough, suggesting that Chortis began to move east before the Cayman began to open.
In concert with the migration of Chortis, initiation of Tertiary arc magmatism in southwest Mexico has migrated east as well (figure 1, green), because the migration of Chortis has allowed the 150-kilometer depth contour of the Farallon-Cocos Benioff Zone to advance eastward beneath southern Mexico.
♦ Finally, Cretaceous passive margin sections of Yucatán, the Bahamas, Colombia, Venezuela and Trinidad transform upward with east-younging diachroneity into tectonically active foreland basins with “arc-bearing” turbiditic flysch (figure 1, ticked basin outlines).
These transformations from passive to active margin (recording first Caribbean collision and subsequent advance) young from west to east at about 20 mm/year, which is, appropriately, the average rate of Atlantic seafloor spreading through time.
GPS measurements confirm the continuation of the 20mm/year rate today.
In summary, the Caribbean’s Pacific origin is perfectly clear. It also is the simplest model, with the Caribbean being fixed in the hot spot reference frame; surely no one can doubt the westward drift of the Americas.
We can constrain Caribbean-American interactions quite well since Santonian, just before the Caribbean Arc collided with the passive margins of northern Colombia and southern Yucatán. Central Caribbean Coniacian abyssal shales, with up to 5 percent TOC, may be time-equivalent to Villeta-La Luna-Querecual-Naparima Hill shelf sections of northern South America, but the relatively thin Caribbean source rock layers pertain to regional or global oceanic anoxic events, partly controlled by mid-Cretaceous Caribbean plume volcanism, and are not strictly correlative.
There remains no hint of continental crust or salt in the deep Caribbean interior, and any Jurassic section, if present, will comprise Pacific pelagics, as in Puerto Rico.
Among the true paleogeographic questions today is not IF the Caribbean is Pacific derived, but HOW and WHEN west-dipping subduction of Proto-Caribbean crust began such that an isolated swath of Pacific lithosphere became engulfed between the westward-drifting Americas.
Historical Highlights is an ongoing EXPLORER series that celebrates the "eureka" moments of petroleum geology, the rise of key concepts, the discoveries that made a difference, the perseverance and ingenuity of our colleagues – and/or their luck! – through stories that emphasize the anecdotes, the good yarns and the human interest side of our E&P profession. If you have such a story – and who doesn't? – and you'd like to share it with your fellow AAPG members, contact Hans Krause.